Energy and load management for data centers is a major client issue. These management issues pose complex problems since data centers use many different types of data storage and file sharing systems, each having their own strengths and weaknesses. For example, data centers may use Network File Systems (NFS) and/or cloud computing paradigms, each requiring load management schemes to make them more efficient. However, various schemes used for load management such as, for example, round robin techniques, closest geographic vicinity schemes, and random location schemes, amongst other schemes, do not take into account energy management issues.
In recent years there have been advances in RAM technology. For example, newer memories, e.g., Phase change Memory, may be better at some properties but cannot replace the existing technologies completely. For this reason, amongst others, all the RAM technologies have to co-exist in the same architecture or system leading to a hybrid structure. RAM technologies are discussed below, in order to provide a basic understanding of such technologies.
Static Random Access Memory (SRAM) is a type of semiconductor memory such that it does not need to be periodically refreshed. However, semiconductor manufacturing process scaling increases leakage which is problematic for SRAM. As a result of continued scaling of MOS transistors, power dissipation due to leakage currents has increased dramatically and is a source of concern especially for low power applications. However, the read and write speed over SRAM are the fastest and thus SRAM gives us the best I/O performance even though at the cost of the increased power leakage.
Embedded Dynamic Random Access Memory (eDRAM) is a capacitor-based dynamic random access memory usually integrated on the same die or in the same package as the main ASIC or processor. Since capacitors leak charge, the information eventually fades unless the capacitor charge is refreshed periodically. Due to the constant refresh, the power consumption as well as the power leakage is high. However, this power leakage is lower than the SRAM leakage. Moreover, the I/O performance is less than that of SRAM but is better than other RAM technologies.
Phase-change memory (also known as PCM, PRAM, PCRAM, Ovonic Unified Memory, Chalcogenide RAM and CRAM) is a type of non-volatile computer memory. PRAM uses the unique behavior of chalcogenide glass, which can be “switched” between two states, crystalline and amorphous, with the application of heat. The contact between the hot phase-change region and the adjacent dielectric is a concern. For example, the dielectric may begin to leak current at higher temperature; however, this power leakage is very low as compared to other technologies. But comparing the read and write speed with the other RAM technologies, it is observed that PRAM has very slow I/O performance.
Magnetoresistive Random Access Memory (MRAM) stores data as electric charge or current flows, but by magnetic storage elements. The elements are formed from two ferromagnetic plates, each of which can hold a magnetic field, separated by a thin insulating layer. One of the two plates is a permanent magnet set to a particular polarity, and the other plate has a field which changes to match that of an external field. Since MRAM is a non-volatile memory technology, there is no power supply to each MRAM cell such that MRAM cells do not consume any standby leakage power. Therefore, the only leakage power is the circuit leakage power for MRAM caches, which is low compared to the total leakage power for other cache technologies. Even though the power leakage is least, the performance is not very comparable with DRAM or SRAM. Moreover, it is observed that sequential memory access requires less power as compared to random memory access.